Strictly Bandlimited ISI-Free Transmission over Intensity-Modulated Channels

Abstract

In this paper, the design and analysis of a new bandwidth-efficient signalling method over the bandlimited intensity-modulated direct-detection (IM/DD) channel is proposed. The channel can be modeled as a bandlimited channel with nonnegative input and additive white Gaussian noise. Due to the nonnegativity constraint, the methods previously proposed for conventional bandlimited channels cannot be applied here. We propose a method to transmit without intersymbol interference in a narrower bandwidth compared to previous works, by combining Nyquist pulses with a constant bias. In fact, we can transmit with a bandwidth equal to that of coherent transmission. A trade-off between the required average optical power and the bandwidth is investigated. At low bandwidths, the most powerefficient transmission is obtained by either the parametric linear pulse or the so-called "better than Nyquist" pulse, depending on the exact bandwidth.

Bandwidth Efficient Root Nyquist Pulses for Optical Intensity Channels

“…Although this eliminates the possibility of finding bandwidth limited root Nyquist pulses, potential still exists to find bandwidth efficient pulses for these channels. Pulses can be shaped such that most of the energy is concentrated in the band of interest [16]. Section 2 presents the discussion on root Nyquist pulse and shows that they are strictly time limited to a single symbol interval.…”